Normally-Off HEMT with P-Type Metal Oxide Gate
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Solution Overview
Problem
Conventional normally-off field-effect semiconductor devices, such as HEMTs and MESFETs, face challenges with high turn-on resistance and gate leak current, and are prone to manufacturing errors and physical defects in the insulating film, leading to inconvenient complexity and expense in circuitry.
Innovation Solution
A field-effect semiconductor device with a metal oxide semiconductor film of p-type conductivity is introduced between the gate electrode and the semiconductor region, creating a depletion zone to maintain the device in a normally-off state, while also reducing gate leak current and enhancing carrier depletion, using nickel oxide and a gate field plate to mitigate field concentrations and stabilize the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a recess is formed in the electron supply layer to create a normally-off HEMT, then the device can be turned off without negative power supply, but the threshold voltage becomes very low (one volt or less) and changes substantially with manufacturing errors in recess depth
Solution Approach 1:
An insulating film (strontium titanate or similar) is introduced as an intermediary between the gate electrode and the electron supply layer. This intermediary allows the gate to be positioned in a recess while providing electrical isolation, enabling the gate to effectively control the 2DEG layer without direct contact, thus achieving normally-off operation with improved threshold voltage stability against manufacturing variations.
Solution Approach 2:
The invention changes the electrical parameters by introducing an insulating film with specific dielectric properties between the gate and electron supply layer. This modification alters the electric field distribution and potential profile, enabling the device to maintain a stable threshold voltage that is less sensitive to recess depth variations while still achieving normally-off operation.
2Reliability
If the gate is accommodated in a recess via an insulating film to achieve normally-off operation, then current leakage is reduced and transconductance is improved, but the insulating film is susceptible to physical defects causing device destruction and current collapse
Solution Approach 1:
The electron supply layer is designed with non-uniform thickness, being thinner in the region underlying the gate electrode and thicker in other regions. This local variation in thickness creates a spatially differentiated structure where the thinner region allows effective gate control and normally-off operation, while the overall structure maintains sufficient electron supply capability, thereby reducing current leakage without requiring a thin insulating film that would be prone to defects.
3Ease of operation
If the electron supply layer is made thinner under the gate to create a hiatus in the 2DEG layer, then the device becomes normally off, but the turn-on resistance becomes excessively high due to insufficient electron density in the 2DEG layer
Solution Approach 1:
The electron supply layer is designed with non-uniform thickness, being thinner in the region underlying the gate electrode and thicker in other regions. This local variation in thickness creates a spatially differentiated structure where the thinner region allows effective gate control and normally-off operation, while the overall structure maintains sufficient electron supply capability, thereby reducing current leakage without requiring a thin insulating film that would be prone to defects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves significantly reduced turn-on resistance and gate leak current, improved antivoltage strength, and stability, allowing for efficient operation with a positive threshold voltage and enhanced current handling capabilities.
Implementation Method 1
a metal oxide semiconductor film disposed between the gate electrode and the main semiconductor region and having a conductivity type (e.g., p-type or n-type) such that carrier concentration in the two-dimensional carrier gas layer is reduced. Namely, the metal oxide semiconductor film has a conductivity type such that the charge carriers are sent away from under the semiconductor film, with the consequent creation of a depletion zone in the two-dimensional carrier gas layer.
Implementation Method 2
By being placed on the electron transit layer having a greater lattice constant, the electron supply layer generates an expansive strain or tensile stress and so undergoes piezoelectric depolarization.
Implementation Method 3
The electron supply layer is additionally subject to spontaneous depolarization.
Data Source
AI summary
A HEMT-type field-effect semiconductor device has a main semiconductor region comprising two layers of dissimilar materials such that a two-dimensional electron gas layer is generated along the heterojunction between the two layers. A source and a drain electrode are placed in spaced positions on a major surface of the main semiconductor region. Between these electrodes, a gate electrode is received in a recess in the major surface of the main semiconductor region via a p-type metal oxide semiconductor film whereby a depletion zone is normally created in the electron gas layer, with a minimum of turn-on resistance and gate leak current.